Ozone pollution is invisible but more terrible than PM2.5, which may cause many kinds of harm to human body.
Our reporter Li Muming
Compared with the "snarling" smog, ozone is much more "low-key" and quietly "hidden" in the clear sky of Wan Li, but it has become the culprit of atmospheric environmental pollution in many cities since it was included in the monitoring indicators in summer in recent years. Statistics of air quality in 74 cities across the country show that among all the days exceeding the standard in June 2015, the days with ozone as the primary pollutant were the most, exceeding the days with PM2.5 as the primary pollutant. In response, on July 23, Guangdong Province announced the air quality of urban environment in the second quarter of 2015, and ozone became the most common primary pollutant; According to media reports, ozone replaced PM2.5 as the primary air pollutant in nearly half of the pollution days in Beijing, Tianjin and Hebei from June to August.
Why is PM2.5, which is well known and concerned by the public, "surpassed" by ozone? What harm does ozone do to human body?
1. "Low-key" ozone is more terrible than PM2.5
Experts believe that the invisible pollution of ozone should not be underestimated, and comprehensive measures should be taken to prevent it, just like smog.
"In fact, ozone pollution has become a new environmental protection issue that plagues the whole country." Wang Yuesi, a researcher at the Institute of Atmospheric Physics, Chinese Academy of Sciences, said. At present, from a national perspective, there is one peak of ozone pollution in the north, while there are two peaks in the south every year. Even Xinjiang, Tibet and other regions are facing ozone pollution problems.
Compared with physical pollution such as black and smelly water pollution, yellow and black smoke pollution with pungent smell, and smog pollution mixed with fine particles, the public and even the environmental protection department have always taken colorless and odorless ozone pollution lightly.
But ozone is actually more terrible than PM2.5
Ozone can react with almost any biological tissue and is very destructive to the respiratory tract. According to the Canadian Center for Occupational Health and Safety (CCOHS), "ozone can irritate and damage the nasal mucosa and respiratory tract, which can cause chest tightness, cough, sore throat, asthma, aggravation of upper respiratory tract diseases, and may also lead to weakened lung function, emphysema and lung tissue damage, and these injuries are often irreparable." Therefore, for people with asthma, emphysema and chronic bronchitis, as long as they are exposed to low-concentration ozone, they may have obvious harm.
Similarly, ozone can also irritate the eyes, reducing visual sensitivity and vision. It will also destroy vitamin E in the skin and make the skin wrinkle and black spots. When the ozone concentration is above 200 μ g/m3, it will damage the central nervous system, causing headaches, chest pains and decreased thinking ability.
In addition, ozone will hinder the function of blood oxygen transmission, resulting in tissue hypoxia; Impairment of thyroid function and calcification of bones. Professor Paul Wentworth of Scripps Institute of Applied Science in the United States has done research and found that ozone can destroy the immune function of human body, induce chromosome aberration of lymphocytes, damage the activity of some enzymes and produce hemolytic reaction.
Even for plants, ozone is not a welcome good thing. Biologists from the University of Valencia, Spain, published a paper in 2006, suggesting that ozone will reduce the concentration of chlorophyll, carotenoids and carbohydrates in plants, which will affect photosynthesis and thus reduce the yield of crops.
2. The most dangerous population: pregnant women and children.
Because the proportion of ozone is about 1.66 times that of air, it often gathers in the lower space, so small children are the most direct victims.
Scientists in Southern California have conducted a five-year follow-up survey on 3,535 children aged 10 to 16, and found that in areas with high ozone concentration (the annual average concentration is between 112 and 138μg/m3), the incidence of asthma in children who often play three or four kinds of sports is twice as high as that in children who do not exercise. Especially, children with low birth weight or premature infants are more likely to be affected by ozone.
If the pregnant woman is exposed to ozone during pregnancy, the baby born may have congenital blepharoptosis (also called congenital microphthalmia, which is usually caused by the unsatisfactory development of fetal eyeball during the third month of pregnancy).
Another study called AHSMOG is aimed at adults. This study, which began in 1977, followed up 3091 adult non-smoking Americans aged 27-87 for 15 years. The results showed that men who were often exposed to ozone showed symptoms of lung damage. In addition, the incidence and mortality of lung cancer were closely related to long-term exposure to ozone.
3. The most dangerous place: the aircraft cabin.
Since ozone is so harmful, when is its high incidence?
According to the "State Key Laboratory of Organic Geochemistry" of Chinese Academy of Sciences, the timeliness and seasonality of ozone are obvious. The ozone concentration is very low in the early morning. After 8 o’clock, with more and more waste gas forming ozone and longer sunshine time, the ozone concentration gradually increases, reaching the peak between 14 o’clock and 16 o’clock, then slowly decreasing, and finally returning to the lowest state after 8 o’clock in the evening. During the year, the peak of ozone concentration is concentrated in summer. During this period, the formation of ozone can be described as "the right time, the right place and the right people": strong sunshine, less clouds and weak wind. This is the reason why people have throat, eyes and nose discomfort when they play when it seems sunny.
In terms of regional distribution, the ozone concentration in urban suburbs and scenic spots is often higher than that in the city center, especially when the suburbs are in the downwind of the city. In this regard, the experts’ explanation is that ozone is particularly lively and will continue to react with other pollutants after it is formed. Therefore, the increasing pollution discharge in the city center will temporarily "eat" ozone, turn it into other pollutants, and then drift to the suburbs with the wind and change it back into ozone. That is to say, even if the ozone concentration measured in the urban area is better than that in the suburbs, there is nothing to be proud of, which mostly shows that there are too many other pollutants in the urban area, which temporarily mutates the ozone.
The urban area is also polluted, and the scenic spots in the suburbs can’t escape. Where else can we stay? The advice of the World Health Organization (WHO) is: "Try not to expect to be outdoors when the ozone is high."
According to the test of the Environmental Protection Agency (EPA), the ozone concentration indoors is generally 50% lower than that outdoors. If the room is well sealed and air conditioning system is adopted, the ozone concentration will be even lower. However, sparks from motor operation, xerography and the working process of TV set will turn some oxygen in the air into ozone. Therefore, mechanical and electrical rooms, electrostatic copier rooms, computer rooms, etc. are all places with high ozone incidence, but attention should be paid to ventilation.
There is also an "indoor" where ozone is concentrated-the airplane cockpit. The ozone in the engine room mainly comes from the atmospheric environment, and the ozone layer is mainly distributed in the atmosphere at an altitude of 10 km to 50 km, while the flying height of civil aircraft is generally 7 km to 12 km.
Modern large passenger planes are equipped with ozone removal systems, but it is still impossible to kill them all. The Canadian side has tested that when the Boeing plane flies at an altitude of 11,895 meters, the external ozone concentration is 3.57mg/m3, and the ozone concentration in the aircraft cabin is 0.29mg/m3. According to a survey funded by the Federal Aviation Administration (FAA), the ozone content in the cockpit of Boeing 747, 727, 737, DC10 and DC9 is relatively high, and the ozone content in the cockpit of long-range aircraft is higher than that of short-haul aircraft. The leader of this survey is William nazarov, an environmental engineer at the University of California. He believes that the solution to the ozone problem in the cockpit is simple, that is, adding an ozone converter to the aircraft. "Unfortunately, not all airlines have this awareness, especially for old and small aircraft. Airlines are more concerned about flight safety."
4. How does ozone pollution come about?
Due to the increasingly obvious harm of ozone, the international safety standards for ozone are becoming stricter and stricter. The "maximum 8-hour daily average" of ozone stipulated by the European Union has dropped to 60nmol/mol (about 120 μ g/m3) in 2010, and the average number of days in a year cannot exceed this standard for more than 25 days. China’s newly revised Ambient Air Quality Standard in 2012 also added the ozone control standard: the daily maximum 8-hour average value is 100 μ g/m3 for Grade I and 160 μ g/m3 for Grade II.
However, it is impossible to assign a general safety value to everyone. "Personal physique, exercise frequency, time spent outdoors, and other pollutants in the air will all affect the harm degree of ozone, which is the headache for the research department." Professor Jerry Martin from the School of Public Health of the University of California explained, "More and more studies have proved that even if the ozone concentration is low, if the human body is exposed for a long time (6-8 hours), the harm will be equally serious. Moreover, ozone will also work in conjunction with other pollutants. For example, ozone will enhance the harm of PM (inhalable particulate matter) to the human body, and PM will also enhance the harm of ozone. "
"It is better to call it photochemical pollution than ozone pollution. Primary pollutants, such as volatile organic pollutants (VOCs) and nitrogen oxides (NOx), which are discharged into the atmosphere by pollution sources such as automobiles and factories, absorb the energy of sunlight under strong ultraviolet irradiation, so that the original chemical chain is destroyed and photochemical reactions occur, resulting in secondary pollutants such as ozone and peroxyacetyl nitrate (PAN). The mixture of primary pollutants and secondary pollutants involved in the photochemical reaction process is called photochemical smog. Ozone is the main component of photochemical smog. When people monitor these pollutants, ozone concentration is also the most important indicator. " China Meteorological Bureau introduced this in its official blog.
5. The governance is difficult, and the top-level design needs to be strengthened.
Ozone pollution is an international topic. After decades of treatment in Los Angeles, the situation has greatly improved, but ozone still exceeds the standard for several days every year. Different from the single ozone pollution in the United States, ozone and PM2.5 are intertwined and interact in China, and it is just starting, so it is more difficult to control.
At the same time, it is not easy to monitor ozone. Wen Yanping, director of Taiyuan Environmental Monitoring Center, said that volatile organic compounds are one of the important precursors of ozone. However, the monitoring work has just started, and its sources and emissions are still in the stage of research and analysis, investigation and research, and its control is also in a state of no standard in the country, immature technology and conscious enterprise.
In addition, ozone monitoring does not have standard gas like sulfur dioxide, so it can easily check the error of monitoring equipment, and it can only take the equipment to Shanghai and other cities to "test the equipment with equipment", which will affect the monitoring of ozone.
Comprehensive control measures of ozone pollution need further research and exploration. Wang Yuesi said that the formation mechanism of ozone is a nonlinear process. Precursors, such as volatile organic compounds (VOCs) and nitrogen oxides (NOx), which can promote ozone generation, must be treated first to control ozone. However, the atmospheric ozone concentration will be effectively reduced only if it is reduced in proportion, which is not easy to handle at present. If only one kind is reduced, it is possible that the ozone concentration will increase instead.
The Air Pollution Prevention Action Plan issued by the State Council in 2013 clearly stated that it is necessary to "strengthen the research on the formation mechanism, source analysis, migration law, monitoring and early warning of haze and ozone, and provide scientific support for pollution control". Experts in the industry believe that governments at all levels must attach great importance to ozone pollution, a new environmental protection topic, and should take comprehensive control measures on the basis of strengthening basic research and top-level design.
Environmental experts say that ozone prevention and control first needs top-level design. Chai Fahe, vice president of china environmental science Research Institute, and others believe that ozone precursors should be included in the national emission reduction targets, and a total control plan for volatile organic compounds and nitrogen oxides should be formulated. Chai Fahe said that ozone precursor is also a kind of precursor of PM2.5 secondary particles. Ozone and PM2.5 treatment should be combined, and comprehensive consideration should not be made. In addition, since ozone pollution is a photochemical pollution, the pollution is aggravated when the temperature is high, so ozone should also be considered when considering global warming.
Wang Yuesi also suggested the implementation of comprehensive regional management. Ozone precursors are highly mobile substances, and nitrogen oxides produced in one area may not be felt by local people, but float to other places to form ozone. The effect of ozone control in a single city will not be too obvious, and regional prevention and control mechanisms should be established in areas with serious ozone pollution such as five provinces in North China, Yangtze River Delta and Pearl River Delta.
Chai Fahe said that the proportion of ozone precursors is different in different places, and even in the same city, the proportion between urban and suburban areas is different. All localities should make clear the ozone formation mechanism in different places, and find out the specific proportion of ozone precursors and the location of emission sources through monitoring, so as to "prescribe the right medicine". And this work needs the cooperation of environmental protection departments and scientific research institutions.
Experts also believe that from the technical level, the focus of ozone precursor control should be on "vehicles, oil, roads and factories": improving automobile exhaust emission standards, improving automobile exhaust devices and reducing emissions; Improve fuel quality; At the same time, gradually switch buses and taxis to gas; Control traffic congestion; Eliminate backward production capacity and control nitrogen oxides and volatiles emitted by coal-fired power plants, cement, coatings, ink printing plants and other enterprises.
Top-level design doesn’t mean that it has nothing to do with the general public. Do a little thing that everyone can do to protect the health of themselves and their families. The development of human society will always rise in a spiral curve. As long as we don’t escape and give up, there are always more ways than problems.
◆ Small information
Ozone is just one word short of oxygen that sustains human life, and one more o, but it is the difference between graphite and diamond. Yes, these two groups of things, which are as different as heaven and earth, are allotropes, that is, simple substances made of the same single chemical element but with different properties.
Because there is one more oxygen atom than oxygen, ozone is more oxidizing than oxygen. What is oxidation? The cut apple will turn brown after a while because it is oxidized by oxygen in the air; The girls’ tender faces are getting older day by day, which is the result of her body oxidation. Ozone is more oxidizing than oxygen. To what extent? Have you smelled chlorine in tap water and swimming pool? That’s for disinfection. It needs to be disinfected with ozone, which is stronger than chlorine. Therefore, the upper floors of household disinfection cabinets are disinfected by ozone.
Walking on the busy streets, we sometimes feel that the air is light brown with a pungent smell, which is commonly called photochemical smog, and ozone is one of the most important components in it. There are a lot of nitrogen oxides and volatile organic compounds in automobile exhaust and factory smoke, which combine with oxygen in the air and form ozone under the catalysis of sunlight radiation and temperature.